1. Field of the Disclosure The present invention relates to a semiconductor compound having the general formula AxB1-xCy, to a method of optimizing positions of a conduction band and a valence band of a semiconductor material using said semiconductor compound, and to a photoactive device comprising said semiconductor compound.
2. Description of the Related Art
Photoelectrochemical cells based on sensitisation of nanocrystalline TiO2 by molecular dyes (so called dye-sensitised solar cells, DSSC) have been first reported by B. O'Regan and M. Grätzel, Nature 353 (1991) 737; WO 91/16719 [1] and have been continuously improved over the last decade. In operation, absorption of a photon leads to the excitation of an electron, which is then injected from the dye molecule into the conduction band of the TiO2 and transported to the front electrode. The dye molecule is regenerated from a platinum counter electrode via a redox couple in electrolyte. Most crucial for a further success of dye-sensitised solar cells is to increase their power conversion efficiency. It depends on short circuit current density JSC, fill factor FF, and the open circuit voltage VOC. JSC depends among others, on the number of absorbed photons and the efficiency to convert those absorbed photons into photoelectrons. FF mainly depends on the conductivity of the materials in use. VOC is dependent on both the energy difference between the conduction band of the semiconducting material and the redox potential of the redox couple as well as the recombination rate of electrons from the semiconductor into the electrolyte (FIG. 1). Most effort has been taken in the past to increase JSC by means of different dye molecules and light management. VOC was increased by means of co-adsorption of smaller molecules together with the dye molecules to suppress recombination. No improvement by changing the semiconductor material or the redox-couple has been reported. Core-shell structures with oxide materials other than TiO2 on the surface of the TiO2 particles partly increased the efficiency ([2] Y. Diamant, S. Chappel, S. G. Chen, O. Melamed, A. Zaban, Coordination Chemistry Reviews 248, 1271 (2004)) but must be regarded as another way of surface treatment.